The present invention is generally directed to battery hydrometers and more particularly to a battery hydrometer which provides an analog output electrical signal related to the specific gravity of the battery electrolyte and therefore related to the state of charge of the battery.
Battery hydrometers for indicating whether a battery is adequately charged or in need of recharging have taken many forms. In one form, an elongated light transmitting rod having an external viewing surface and a conical tip arranged to be disposed beneath the surface of the electrolyte is associated with a float, generally a ball of a bright color, confined within an open walled cage. The cage is carried at the end of the rod and is arranged to dispose the float in two different positions relative to the rod tip depending upon the specific gravity of the battery electrolyte. In one position, the ball is immediately adjacent the tip and viewable through the indicating surface. This indicates that the specific gravity of the electrolyte is above a predetermined specific gravity and that the battery is therefore not currently in need of recharging. In the other position, the float is guided by the cage downwardly and away from the tip so that it is no longer viewable through the indicating surface. This indicates that the electrolyte specific gravity is now below the predetermined value and that the battery is in need of recharging.
Such hydrometers have been found to be very accurate because the specific gravity of a battery electrolyte exhibits the most reliable relationship to the state of charge of a battery. However, hydrometers of this type are not suited for remote indication, as for example, on the dashboard of an automobile or the like. Further, they indicate only two states of battery charge, one where the battery requires recharging, and the other where the battery has adequate charge.
In an attempt to overcome these deficiencies, hydrometers have been proposed which utilize the same float technique. These hydrometers incorporate a light source and detector to remotely indicate which of the two positions the float is at. On such hydrometer is fully described and claimed in U.S. Pat. No. 3,954,010 which is assigned to the assignee of the present invention. In one position, the float totally blocks the light to the detector and in the other position, the float is out of the way of the light. While monitors of this type do provide remote indication, they still provide an indication of only the two battery charge states indicated by the first mentioned hydrometers.
With renewed interest in battery powered vehicles of all types, there has become a recognized need for an even more improved battery hydrometer which not only provides for remote indication, but which also provides an analog output. Most desirably, an analog output should indicate every battery charge state between and including full battery charge and no battery charge. As a result, such a battery hydrometer would facilitate the use of a remote dashboard meter capable of indicating energy consumption in a manner similar to conventional fuel guages.
It is therefore a general object of the present invention to provide a new and improved battery hydrometer.
It is a further object of the present invention to provide a battery hydrometer which facilitates remote indication while also providing an analog output signal having a magnitude related to the state of charge of a battery.